The present invention relates to a method and apparatus for controlling the fuel-feeding rate of an internal combustion engine during starting of and for a period of time after starting of the engine.
In an internal combustion engine of the electronic fuel-injection control type having fuel injection valves or of the electronic carburetor-control type having an electronically controlled carburetor, not only is a normal warm-up enrichment operation for increasing the fuel-feeding rate depending upon the warm-up condition (coolant temperature) of the engine executed but an engine-starting enrichment operation for additionally increasing the fuel-feeding rate during starting (cranking) of the engine is also executed. When the coolant temperature exceeds a predetermined temperature, the above-mentioned additional increment according to the starting-enrichment operation is gradually decreased to the normal increment in accordance with the lapse of time. Thereafter, the normal warm-up enrichment is executed. These enrichment operations (hereinafter referred to as two-characteristic enrichment) are already known by, for example, SAE paper No. 740,020, pages 237 to 244.
During starting of the engine and for a period of time after starting of the engine, since the temperature of the inner wall in the combustion chamber is low, the engine requires a rich air-fuel mixture in order for good operating characteristics to be obtained. Therefore, during starting of and for a while after starting of the engine, the above starting-enrichment operation is carried out. However, since the inner wall temperature rises faster than the coolant temperature, which is, in general, used for detecting the warm-up condition of the engine, the starting-enrichment operation need not be executed until the engine is fully warmed-up. Accordingly, when the coolant temperature rises higher than a predetermined temperature during starting and after starting of the engine, the starting increment of the fuel-feeding rate is gradually decreased to the normal increment, according to the normal warm-up enrichment operation, with the lapse of time, causing the emission control characteristics to improve.
However, according to the above-mentioned conventional two-characteristic enrichment, since transfer from the starting enrichment to the normal warm-up enrichment starts depending upon the coolant temperature, if the detected coolant temperature is not accurately representative of the actual warm-up condition of the engine, problems occur. In general, the coolant-temperature sensor is located in the area of the engine block near the outlet of the coolant passage. The coolant temperature near the coolant passage outlet is not representative of the warm-up condition but is representative of the environment temperature at a time just after the engine is started. Therefore, if the environment temperature is higher than a predetermined temperature, the starting increment decreases irrespective of the low-inner wall temperature of the combustion chamber. Thus, appropriate fuel increment corresponding to the inner wall temperature of the combustion chamber cannot be expected according to the prior control technique.